Immunoaffinity trapping of urinary human chorionic gonadotropin and its high-performance liquid chromatographic-mass spectrometric confirmation

Affinity capture in bottom-up protein analysis - Overview of current status of proteolytic peptide capture using antibodies and molecularly imprinted polymers

Antibody-based affinity capture has become the gold standard in sample preparation for determination of low-abundance protein biomarkers in biological matrices prior to liquid chromatography-mass spectrometry (LC-MS) determination. This comprises both capture of intact proteins prior to the digestion step and capture of proteolytic peptides after digestion of the sample. The latter can be performed both using antibodies specifically developed to capture target proteolytic peptides, as well as by the less explored use of anti-protein antibodies to capture the proteolytic epitope peptide. Molecularly imprinted polymers (MIPs), also called plastic antibodies are another affinity-based approach emerging as sample preparation technique in LC-MS based protein biomarker analysis. The current review gives a critical and comprehensive overview of proteolytic peptide capture using antibodies and MIPs in LC-MS based protein biomarker determination during the last five years. The main emphasis is on capture of non-modified peptides, while a brief overview of affinity capture of peptides containing post-translational modifications (PTMs) is provided.

Identification and semi-relative quantification of intact glycoforms of human chorionic gonadotropin alpha and beta subunits by nano liquid chromatography-Orbitrap mass spectrometry

The human chorionic gonadotropin (hCG) protein belongs to a family of glycoprotein hormones called gonadotropins. It is a heterodimer made of two non-covalently linked subunits. The α-subunit structure, hCGα, has 2 N-glycosylation sites, while the beta subunit, hCGβ, has 2 N- and 4 O-glycosylation sites. This leads to numerous glycoforms. A method based on the analysis of hCG glycoforms at the intact level by nano-reversed phase liquid chromatography coupled to high resolution mass spectrometry (nanoLC-HRMS) with an Orbitrap analyzer was previously developed using a recombinant hCG-based drug, Ovitrelle®, as standard. It allowed the detection of about 30 hCGα glycoforms, but didn't allow the detection of hCGβ glycoforms. This method was thus here significantly modified (addition of a pre-concentration step of the sample to increase the sample volume from 70 nl to 1 µl, optimization of the gradient slope and the nature and content of the acidic additive in the mobile phase). It led to an improvement of the separation of hCGα and hCGβ glycoforms, which allowed for the first time the detection of 33 hCGβ glycoforms at intact level. In addition, a higher number of hCGα glycoforms (42 in total, i.e. a 40% increase) was detected. The figures of merit of this new method were next assessed. The relative standard deviations (RSDs) of the retention time ranged between 0.02 and 0.95% (n = 3), with an average value of 0.36% for the alpha glycoforms and between 0.01 and 1.08% (n = 3) with an average value of 0.23% for the beta glycoforms. The RSDs of the relative peak area measured on the extracted ion chromatogram of each glycoform were below 20% (n = 3), with an average value of 9.8%, thus allowing semi-relative quantification. Therefore, this method has a high potential for rapid quality control aiming for the detection and comparison of glycoforms present in glycoprotein-based pharmaceutical preparations.

Immunoextraction-tandem mass spectrometry method for measuring intact human chorionic gonadotropin, free β-subunit, and β-subunit core fragment in urine

BACKGROUND

Human chorionic gonadotropin (hCG) stimulates testosterone production by the testicles. Because of the potential for abuse, hCG is banned (males only) in most sports and has been placed on the World Anti-Doping Agency list of prohibited substances. Intact hCG, free β-subunit (hCGβ), and β-subunit core fragment (hCGβcf) are the major variants or isoforms in urine. Immunoassays are used by antidoping laboratories to measure urinary hCG. Cross-reactivity with isoforms differs among immunoassays, resulting in widely varying results. We developed a sequential immunoextraction method with LC-MS/MS detection for quantification of intact hCG, hCGβ, and hCGβcf in urine.

METHODS

hCG isoforms were immunoextracted with antibody-conjugated magnetic beads and digested with trypsin, and hCGβ and hCGβcf unique peptides were quantified by LC-MS/MS with the corresponding heavy peptides as internal standard. hCG isoform concentrations were determined in urine after administration of hCG, and the intact hCG results were compared to immunoassay results.

RESULTS

The method was linear to 20 IU/L. Total imprecision was 6.6%-13.7% (CV), recovery ranged from 91% to 109%, and the limit of quantification was 0.2 IU/L. Intact hCG predominated in the urine after administration of 2 hCG formulations. The window of detection ranged from 6 to 9 days. Mean immunoassay results were 12.4-15.5 IU/L higher than LC-MS/MS results.

CONCLUSIONS

The performance characteristics of the method are acceptable for measuring hCG isoforms, and the method can quantify intact hCG and hCGβ separately. The limit of quantification will allow LC-MS/MS hCG reference intervals to be established in nondoping male athletes for improved doping control.

Precise measurement for the purity of amino acid and peptide using quantitative nuclear magnetic resonance

Precise measurement for the purity of organic compounds will fundamentally improve the capabilities and measurement services of the organic chemical analysis. Quantitative nuclear magnetic resonance (qNMR) is an important method to assess the purity of organic compounds. We presented a precise measurement method for the purity of small molecule with identification of impurities. In addition, the qNMR was rarely applied to purity of large compounds such as peptide, for which qNMR peaks are too crowded. Other than general idea of qNMR, we removed unwanted exchangeable peaks by proton exchange, as a new approach for qNMR, to make the quantitative protons of peptide isolated, which can ensure precise measurement. Moreover, a suitable internal standard, acesulfame potassium, was applied. The analytes were valine and peptide T5, due to their importance for protein analysis. For valine, the intraday CV was 0.052%, and the interday CV during 8 months was 0.071%. For peptide T5, simpler operation, shorter analytical time (1h vs. 3 days) and smaller CV (0.36% vs. 0.93%) were achieved by qNMR, compared with a traditional method (amino acid based isotope labeled mass spectrometry) via a hydrolysis reaction. This method has greatly increased the quantitative precision of qNMR for small compounds, and extended application scope of qNMR from small compounds to peptides.

Effects of recombinant human LH and hCG on serum and urine LH and androgens in men

CONTEXT

The administration of gonadotrophins is prohibited in sport but the effect in men of recently available recombinant hCG and LH on serum and urine concentrations of gonadotrophins and androgens has not been systematically evaluated in the antidoping context.

OBJECTIVE

To determine the time-course of recombinant LH (rhLH) and hCG (rhCG) on blood and urine hormone profiles in men to develop effective tests to detect rhLH and rhCG doping.

DESIGN

Two randomized controlled studies with a 2 x 2 factorial design.

SETTING

Academic research centre.

PARTICIPANTS

Healthy male volunteers aged 18-45 years.

INTERVENTIONS

In the rhLH study, men were randomized into (i) either of two single doses of rhLH (75 IU or 225 IU), and (ii) suppression of endogenous LH and testosterone by nandrolone or no suppression. In the rhCG study, men were randomized into (i) either of two single doses of rhCG (250 or 750 microg), and (ii) suppression of endogenous LH and testosterone by nandrolone decanoate (ND) or no suppression. ND suppression comprised a single dose of 200 mg ND 3 days prior to, and in the rhCG study an additional dose 1 day after gonadotrophin injection.

MAIN OUTCOME MEASURES

Serum and urine hCG, LH, T, T : LH ratio, urine epitestosterone (E) and urine T : E ratio.

RESULTS

Neither rhLH dose produced a significant increase in serum or urine LH or T or in the T : E or T : LH ratios regardless of ND-induced suppression of endogenous LH and T. Nor did an even higher dose (750 IU) in three healthy men with unsuppressed gonadal axis. These findings were confirmed with two different commercial LH immunoassays together with adjustment for any influence of urine sediment and dilution. Both rhCG doses produced a steep, dose-proportional increase in serum and urine hCG with increases in serum and urine T and suppression of serum and urine LH, regardless of hCG dose. Serum but not urine T was lowered by ND suppression. The T : LH ratio showed a progressive increase unrelated to rhCG dose or ND suppression, whereas both rhCG and ND suppression minimally increased T : E ratio.

CONCLUSIONS

Both rhCG doses produce a striking increase in serum hCG and T with suppression of serum LH but, at single doses up to 750 IU, rhLH has no influence on serum or urine LH or T. Effective rhLH doping, which relies on a sustained increases in endogenous T, would require much higher and more frequent daily rhLH doses. Use of LH immunoassays optimized for serum to detect rhLH doping by urine LH measurement requires more standardization and validation and, at present, is unreliable. The T : LH ratio is, however, a useful screening test for hCG doping although its utility requires further evaluation.

The analytical chemistry of drug monitoring in athletes

The detection and deterrence of the abuse of performance-enhancing drugs in sport are important to maintaining a level playing field among athletes and to decreasing the risk to athletes' health. The World Anti-Doping Program consists of six documents, three of which play a role in analytical development: The World Anti-Doping Code, The List of Prohibited Substances and Methods, and The International Standard for Laboratories. Among the classes of prohibited substances, three have given rise to the most recent analytical developments in the field: anabolic agents; peptide and protein hormones; and methods to increase oxygen delivery to the tissues, including recombinant erythropoietin. Methods for anabolic agents, including designer steroids, have been enhanced through the use of liquid chromatography/tandem mass spectrometry and gas chromatography/combustion/isotope-ratio mass spectrometry. Protein and peptide identification and quantification have benefited from advances in liquid chromatography/tandem mass spectrometry. Incorporation of techniques such as flow cytometry and isoelectric focusing have supported the detection of blood doping.

Anabolic steroid use: patterns of use and detection of doping

Anabolic-androgenic steroids (AAS) were the first identified doping agents that have ergogenic effects and are being used to increase muscle mass and strength in adult males. Consequently, athletes are still using them to increase physical performance and bodybuilders are using them to improve size and cosmetic appearance. The prevalence of AAS use has risen dramatically over the last two decades and filtered into all aspects of society. Support for AAS users has increased, but not by the medical profession, who will not accept that AAS use dependency is a psychiatric condition. The adverse effects and potential dangers of AAS use have been well documented. AAS are used in sport by individuals who have acquired knowledge of the half-lives of specific drugs and the dosages and cycles required to avoid detection. Conversely, they are used by bodybuilders in extreme dosages with the intention of gaining muscle mass and size, with little or no regard for the consequences. Polypharmacy by self-prescription is prevalent in this sector. Most recently, AAS use has filtered through to 'recreational street drug' users and is the largest growth of drugs in this subdivision. They are taken to counteract the anorexic and cachectic effects of the illegal psychotropic street drugs. Screening procedures for AAS in World Anti-Doping Agency accredited laboratories are comprehensive and sensitive and are based mainly on gas chromatography-mass spectrometry, although liquid chromatography-mass spectrometry is becoming increasingly more valuable. The use of carbon isotope mass spectrometry is also of increasing importance in the detection of natural androgen administration, particularly to detect testosterone administration. There is a degree of contentiousness in the scenario of AAS drug use, both within and outside sport. AAS and associated doping agents are not illegal per se. Possession is not an offence, despite contravening sporting regulations and moral codes. Until AAS are classified in the same capacity as street drugs in the UK, where possession becomes a criminal offence, they will continue to attract those who want to win at any cost. The knowledge acquired by such work can only assist in the education of individuals who use such doping agents, with a view to minimizing health risks and hopefully once again create a level playing field in sport.

Gonadotropins in doping: pharmacological basis and detection of illicit use

Parenteral administration of human chorionic gonadotropin (hCG) or luteinizing hormone (LH) stimulates the production of testosterone in males and these gonadotropins can therefore be used by athletes to enhance muscle strength. However, they are more expensive and less efficient than testosterone and anabolic steroids. Therefore their main use is probably to stimulate gonadal testosterone production during and after self-administration of testosterone or anabolic steroids. A positive effect of hCG on muscle strength has not been demonstrated in women and elevated concentrations of hCG in females are often caused by pregnancy. The use of gonadotropins is therefore prohibited only in males but not in females. HCG occurs at low but measurable concentrations in plasma and urine of healthy males and can be measured by sensitive methods. However, the characteristics of the method to be used for doping control have not been defined. Virtually all commercially available hCG assays have been designed for determination of hCG in serum rather than urine, which is used for doping control. Methods based on mass spectrometric detection of fragments derived from hCG extracted from urine by immunoadsorption have been developed but their suitability for doping control remains to be determined. The concentrations of LH in serum and urine are variable and more then 10-fold higher than those hCG. It is therefore difficult to detect illicit use of LH. The characteristics and reference values for hCG and LH assays used in doping control and the cutoff values need to be defined.

An introduction to mass spectrometry based proteomics-detection and characterization of gonadotropins and related molecules

This review introduces fundamental aspects of mass spectrometry (MS) based proteomics and illustrates how MS is an effective tool for the analysis of glycoprotein hormones. Matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) and electrospray ionization (ESI) MS are complementary approaches that have been applied for the analysis of gonadotropins, e.g. to characterize differences in the oligosaccharide distribution of commercial human chorionic gonadotropin preparations, for isolated nicked beta-subunit, and identification of a metabolite of placental transforming growth factor in pharmaceutical hCG preparations. Immunoaffinity trapping and concentration of digested sample extract prior to MS analysis confers analytical sensitivity akin to immunoassay. A desirable objective would be to develop for clinical purposes a rapid procedure for MS detection and characterization of gonadotropins. Refinement of on-target immobilization and digestion for subsequent ionization by MALDI may eventually help to provide this capability. The advent of hybrid mass spectrometers will further advance the characterization of these complex molecules.

Immunoaffinity extraction and tandem mass spectrometric analysis of human chorionic gonadotropin in doping analysis

A confirmatory and quantitative HPLC-tandem mass spectrometry (MS-MS) method for human chorionic gonadotropin hormone (hCG) at concentrations as low as 5 IU/l following immunoaffinity extraction of the glycoprotein from urine was developed. The extraction method involved retention of urinary hCG in the immunoaffinity column via specific antigen-antibody interaction. A variety of eluents were then used to quantitatively elute hCG from the immunoaffinity column. Qualitative and quantitative analysis of hCG were undertaken using MS-MS by identifying the amino acid sequence of the marker peptide betaT5 obtained from hCG by tryptic digestion and the peak areas of three product ions b(6)(+), b(9)(+) and y(11)(+), respectively.

Miniaturized amperometric flow immunoassay system using a glass fiber membrane modified with anion

This paper describes a miniaturized amperometric flow immunoassay system using a glass fiber membrane modified with anion. The glass fiber membrane was functionally modified with gamma-glycidoxypropyltrimethoxysilane and sodium thiosulfate and was used for separation of protein. Anti-human chorionic gonadotrophin (HCG) immunoglobulin G (IgG) antibody conjugated with ferrocenemonocarboxylic acid (Fc), namely, Fc-conjugated IgG (Fc-IgG), was used as a novel analytical reagent. HCG and Fc-IgG complexes were separated from free Fc-IgG based on differences in isoelectric point (pI) using the glass fiber membrane modified with a thiosulfonyl acid functional group. The assay yields a linear relationship between current and HCG concentration in the range of 0-2000 mIU/mL. This simple technique enables the assay of HCG within 2 min. The modified glass fiber membrane was regenerated by occasional elution with malonate buffer (pH 6.0) containing 0.5 M NaCl, to remove free Fc-IgG. Free Fc-IgG recovered in this manner could be reused up to eight times without significant decreases in sensitivity. This miniaturized amperometric flow immunoassay requires only minute quantities of serum and generates highly reproducible results.

Construction of electrochemical flow immunoassay system using capillary columns and ferrocene conjugated immunoglobulin G for detection of human chorionic gonadotrophin

In this paper is reported a miniaturized flow immunoassay system. Ferrocenecarboxylic acid (Fc) conjugated with anti-HCG immunoglobulin G (IgG) antibody (Fc-IgG) was prepared, and used as a novel analytical reagent. The system consists of the immunoreaction section, the capillary column packed with cation exchange resin, and the flow cell for electrochemical detection of Fc-IgG. Antibody-antigen complexes were separated from their free conjugate on the basis of differences in isoelectric point (pI) using a cation exchange capillary column. The assay yielded a linear relationship between signal and HCG concentration in the range 0-2000 mIU/ml. This simple technique enables the assay of HCG within 2 min. The cation exchange capillary column was regenerated by occasional elution with malonate buffer (pH 6.0) containing 0.5 M NaCl, to remove free conjugate. Free conjugate recovered in this manner could be reused up to eight times without significant decreases in the sensitivity of the immunoassay. This electrochemical flow immunoassay requires only minute quantities of serum and generates highly reproducible results.

Determination of the Glycoforms of Human Chorionic Gonadotropin β-Core Fragment by Matrix-assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry

Background: Metabolism of human chorionic gonadotropin (hCG) in the serum and kidney yields the terminal urinary product hCG β-core fragment (hCGβcf), comprising two disulfide-linked peptides (β6-β40 and β55-β92) of which one (β6-β40) retains truncated N-linked sugars. Hyperglycosylated hCGβcf may indicate choriocarcinoma or Down syndrome, but the glycosylation profile of hCGβcf has not been thoroughly evaluated.

Methods: hCGβcf, purified from pregnancy urine, was reduced by “on-target” dithiothreitol (DTT) reduction and analyzed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). The mass ([M+H]+) of the primary sequence of the glycosylated peptide β6-β40 was subtracted from the m/z values of the discrete peaks observed to give the masses of the carbohydrate moieties. Carbohydrate structure was predicted by sequentially subtracting the masses of the monosaccharide residues corresponding to N-linked carbohydrates of the hCG β-subunit reported in the literature.

Results: Mass spectra of hCGβcf revealed a broad triple peak at m/z 8700–11300. After reduction, the triple peak was replaced by a discrete set of peaks between m/z 4156 and 6354. A peak at m/z 4156.8 corresponded to the nonglycosylated peptide (β55-β92). The remaining nine peaks indicated that urinary hCGβcf comprises a set of glycoforms smaller and larger than the trimannosyl core.

Conclusions: hCGβcf comprises a wider set of glycoforms than reported previously. Peaks of highest mass indicate evidence of hyperglycosylated carbohydrate moieties. The data support previous reports that hCGβcf oligosaccharides lack sialic acid and galactose residues. No indication was found of a β6-β40 peptide that was entirely devoid of carbohydrate.

Definition and measurement of follicle stimulating hormone

FSH has a key role in the development and function of the reproductive system and is widely used both diagnostically and therapeutically in developmental and reproductive medicine. The accurate measurement of FSH levels, in patients for diagnosis and monitoring and in therapeutic preparations for clinical use, is essential for safe and successful treatment. Historically, FSH was defined on the basis of classical in vivo endocrine activity, and early therapeutic preparations were calibrated using in vivo bioassays. There was early recognition that reference preparations were required for calibration if the results from different laboratories were to be comparable. In response to the perceived need, the World Health Organization established the first standard for such preparations in 1959. Subsequent developments in biotechnology have led to recognition that there is no single molecule that can be uniquely defined as FSH, and that FSH can induce a range of biological activities. Several highly purified standards for FSH are now available, but discontinuity and heterogeneity of estimates of FSH activity in terms of these standards made using in vitro assays and binding assays have been noted. It is thus essential that any measurement of FSH include specification both of the standard with which the measured FSH is compared and the assay method used for that comparison.

Liquid chromatography-mass spectrometry: potential in forensic and clinical toxicology

A relatively limited number of papers concerning applications of liquid chromatography-mass spectrometry (LC-MS) to forensic or clinical toxicology, or analytical methods directly applicable to these topics have been published so far, but their number have greatly increased in the past two years, probably due to technical improvements and to a decrease in the price of such instruments. After a brief presentation and exemplary applications of the interfaces and/or sources proposed in the past for coupling HPLC to mass spectrometry (direct liquid inlet, moving belt, fast atom bombardment and thermospray interfaces), this paper describes electrospray-type and atmospheric pressure chemical ionisation interfaces and their most recent applications in forensic or clinical toxicology. In a third section, the different LC-MS solutions proposed for typical applications in human toxicology, such as the determination of morphine metabolites, LSD and its metabolites and corticosteroids in blood or urine, are reviewed in detail in order to highlight the strengths and weaknesses of each ionisation device and/or analytical method. The last section envisages the new analytical fields opened up by LC-MS in toxicology, regarding mainly peptides, proteins and large molecules, as well as the possible use of LC-MS as a complement to GC-MS for "general unknown" screenings; it also deals with the perspectives concerning technical improvements in ionisation interfaces/sources or mass spectrometers, as well as in sample preparation and liquid chromatography techniques applied to this type of coupling. Though LC-MS is still a relatively new technique in toxicology, on taking into consideration its success so far and owing to the simplification of instruments and concept handling thanks to user-friendly software, it is the authors' opinion that it will become a major success in analytical toxicology in the next few years.

Affinity Chromatography: A Review of Clinical Applications

Affinity chromatography is a type of liquid chromatography that makes use of biological-like interactions for the separation and specific analysis of sample components. This review describes the basic principles of affinity chromatography and examines its use in the testing of clinical samples, with an emphasis on HPLC-based methods. Some traditional applications of this approach include the use of boronate, lectin, protein A or protein G, and immunoaffinity supports for the direct quantification of solutes. Newer techniques that use antibody-based columns for on- or off-line sample extraction are examined in detail, as are methods that use affinity chromatography in combination with other analytical methods, such as reversed-phase liquid chromatography, gas chromatography, and capillary electrophoresis. Indirect analyte detection methods are also described in which immunoaffinity chromatography is used to perform flow-based immunoassays. Other applications that are reviewed include affinity-based chiral separations and the use of affinity chromatography for the study of drug or hormone interactions with binding proteins. Some areas of possible future developments are then considered, such as tandem affinity methods and the use of synthetic dyes, immobilized metal ions, molecular imprints, or aptamers as affinity ligands for clinical analytes.

Survey of recent advances in analytical applications of immunoaffinity chromatography

Methods that use immunoaffinity chromatography (IAC) for sample preparation or detection are becoming increasingly popular as tools in the analysis of biological and nonbiological compounds. This paper presents an overview of immunoaffinity chromatography and examines some recent developments of this technique in analytical applications. The emphasis is placed on HPLC-based IAC methods or those that combine IAC with other instrumental techniques; however, novel approaches that employ low-performance IAC columns for chemical quantitation are also considered. Particular applications that are examined include (1) the use of IAC in the direct detection of analytes, (2) the extraction of samples by IAC prior to on- or off-line detection by other methods, (3) the use of IAC in chromatographic-based immunoassays, and (4) the development of postcolumn reactors based on IAC for the detection of analytes as they elute from other types of chromatographic columns. The advantages and limitations for each approach are considered. In addition, a summary is provided of reports in the literature that have used IAC for these various formats.

Athletic drug testing

A drug-control program requires testing to ensure compliance and to deter use. In the athletic drug testing area, measurement of performance-enhancing substances is complex partly because of the large number of prohibited substances. A number of sophisticated analytical techniques, such as high-resolution mass spectrometry, are increasingly used to provide the maximum detection time window. Endogenous steroids pose an increasing challenge because of their availability in "nutritional supplements". Continued vigilance is required to prevent the pharmacologic enhancement of performance.

Epitope mapping of monoclonal antibodies by mass spectrometry: identification of protein antigens in complex biological systems

We describe the application of immunoaffinity extraction and mass spectrometry to the analysis of Ty1 Gag protein in lysates of Saccharomyces cerevisiae. A magnetic bead-conjugated monoclonal antibody was used to achieve selective extraction, the specificity of which was established by matrix-assisted laser desorption/ionization mass spectrometric (MS) analysis of an extract of the lysate of cells overexpressing the Ty1 Gag protein. MS analysis of similar extracts of lysates following tryptic hydrolysis confirmed selective extraction of the epitope-containing peptide fragment. Sufficient sensitivity was achieved to allow the application of this approach to the analysis of lysates of wild-type cells. Furthermore, the sequence of the epitope-containing peptide was confirmed by electrospray-tandem MS. To our knowledge, this constitutes the first report of the application of immunoaffinity extraction and tandem MS analysis to the characterization of an antigen recovered from a complex cellular system.

Mass spectrometric characterization of nicked fragments of the β-subunit of human chorionic gonadotropin

We describe the use of an HPLC/MS technique for the characterization of nicked fragments of hCG β-subunit. After reductive alkylation of the nicked hCG β-subunit with vinylpyridine, endoproteinase Glu-C or trypsin was used to digest the protein to produce peptides that could be analyzed by HPLC/electrospray ionization MS. Human leukocyte elastase digestion was used to produce an experimentally nicked hCG. Two nicking sites were observed, between amino acids 42Thr and 43Arg and between 44Val and45Leu. The former site has not been previously reported for elastase digestion. The structures of the fragments were confirmed by HPLC/MS after removal of the oligosaccharide by direct mass measurement and by mass determination of their proteolytic digests. Without the glycopeptidase treatment, the microheterogeneity of the two N-linked oligosaccharides could be deduced from the spectra of the proteolytic fragments. Nicking with elastase was found to alter the oligosaccharide structures. Nicked β-subunit samples isolated from the urine of choriocarcinoma patients were also analyzed and the location of the nicking site(s) agreed with that determined by classical techniques. Important differences in the oligosaccharide structures were also observed in these samples, including the presence of triantennary oligosaccharides not found in hCG from healthy subjects. These findings demonstrate the potential of HPLC/MS for characterization of glycoprotein standard preparations.

Analytical advances in detection of performance-enhancing compounds

The use and abuse of performance-enhancing substances has been an issue in sports since the ancient Greeks. The availability of numerous synthetic steroids and recombinant peptide hormones has made testing an analytical challenge. Recent advances in mass spectrometry have provided an opportunity to decrease detection limits. The Atlanta Olympic Games in 1996 marked the first time every specimen was screened by gas chromatography (GC) coupled to high-resolution mass spectrometry (MS). A further improvement may be seen with GC/MS/MS and quadrupole ion traps. Electrospray HPLC/MS has also been applied to the detection and confirmation of peptide hormones in urine. The ability to detect subtle differences in oligosaccharide structure may provide a way to detect abuse of recombinant glycoproteins. Simply decreasing detection limits is not enough; new technology also allows development of a foundation on which to base interpretation. Application of HPLC/MS/MS has allowed direct measurement of steroid conjugates in urine. The relative importance of sulfate, glucuronide, and other conjugates and metabolites of testosterone and epitestosterone can now be assessed. In the international sports arena, the impact of genetic metabolic disposition must also be considered if we are to provide an equitable system. Further research will establish more-refined criteria for the detection threshold of abused substances.